Magnetic excitations in theXY-pyrochlore antiferromagnetEr2Ti2O7

Abstract

The XY-pyrochlore antiferromagnet Er2Ti2O7 is studied by heat capacity measurements and electron spin resonance spectroscopy performed on single crystal samples. The magnetic phase diagrams are established for two directions of applied field, H[100] and H [111]. In the magnetically ordered phase observed below TN = 1.2 K, the magnetic excitation spectrum consists of a Goldstone mode acquiring an isotropic gap in an applied field, and another mode with a gap softening in the vicinity of a field-induced phase transition. This second-order transition takes place at a critical field Hc above which the magnetization process is accompanied by a canting of the magnetic moments off their local "easy-planes". The specific heat curves for H [100] (H ≫ Hc) are well described by a model presuming a single dispersionless excitation mode with the energy gap obtained from the spectroscopic measurements.

Holographic antiferromagnetic quantum criticality andAdS2scaling limit

“…The local crystal field (CF) of a trigonal D 3d point symmetry at the erbium sites splits the 16-fold degenerate state into eight doublets. Considering the sum of all these spin doublets associated with the single ion as a single total spin we note that these total spins are ordered in noncoplanar structure on the vertex-sharing tetrahedra [36,37]. The compound has a strong local XY-type anisotropy of magnetic moments arising due to the large orbital momentum of Er 3þ ions, L ¼ 6.…”

“…The detailed measurements of the low-temperature magnetic properties of compound and the analysis of these experimental data leads to the conclusion that the ground state is characterized by exotic spin dynamics [36,37], which is vanishing at the Néel's temperature, T N ¼ 1.2 K, via a second-order phase transition. There the co-existence of both the short-and long-range orders has been suggested.…”

“…To understand the role of magnetic frustrations in establishing long-range order is now one of the main challenges of condensed matter physics. They play probably an important role in the formation of the nontrivial antiferromagnetic non-coplanar structure observed [36,37].…”

“…This is possibly a second-order phase transition. It takes place at a critical field H c above which the magnetization process is accompanied by a canting of the magnetic moments off their local easy planes [36].…”

“…The magnetic excitation spectrum obtained with ESR [36] consists of a Goldstone mode, which has an isotropic gap in an applied field. When the magnetic field increases, there arises a field-induced quantum phase transition.…”